Carbon, nitrogen, and oxygen stable isotope ratios of striped dolphins and short-finned pilot whales stranded in Hokkaido, northern Japan, compared with those of other cetaceans stranded and hunted in Japan

ABSTRACT

Strandings of striped dolphins (SD) and short-finned pilot whales (PW) in Hokkaido, northern Japan, are rare but have recently increased, probably due to global warming. We quantified δ¹³C, δ¹⁵N, and δ¹⁸O in muscles of SD (n = 7) and PW (n = 3) stranded in Hokkaido and compared these values with those in muscles (red meat products) of hunted SD and PW in three areas of central and southern Japan. δ¹⁸O in stranded SD, except for the calf, decreased with increasing body length (BL), whereas δ¹³C increased, with no BL-related changes in δ¹⁵N. The variability of δ¹⁸O (range of maximum and minimum) was larger in the stranded SD (7.5 ‰) than of the hunted SD in three areas (0.9, 1.9, and 1.4 ‰), whereas that of δ¹⁵N was smaller in the stranded SD than in the hunted SD. Similarly, the variability of δ¹⁸O was larger in the stranded PW in Hokkaido (3.3 ‰) than in the hunted PW in central Japan (1.4 ‰). The larger variability of δ¹⁸O and smaller variability of δ¹⁵N in stranded SD imply long-term sojourning in coastal waters and feeding on small amounts of limited prey species at low trophic levels before death.

KEYWORDS:

• Carbon-13
• isotope ecology
• mercury
• migration
• nitrogen-15
• oxygen-18
• short-finned pilot whales (Globicephala macrorhynchus)
• stranding
• striped dolphins (Stenella coeruleoalba)

Acknowledgment

We would like to thank the Stranding Network Hokkaido (SNH) for providing samples and information on the stranded cetaceans investigated in this study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.